The present invention provides an improved process over the process described in U.S. Pat. application Ser. No. 463,329, filed Apr. 23, 1974 now U.S. Pat. No. 3,956,245, issued May 11, 1976, directed to the preparation of random copolymers by the free-radical bulk polymerization of vinyl esters and vinyl aromatic compounds such as styrene. More particularly, the present process provides an improvement over the process described in U.S. Ser. No. 463,329, now U.S. Pat. No. 3,956,245 particularly with regard to the application of the resulting copolymers for coating purposes, especially in non-aqueous dispersions.
For the purpose of the present application, U.S. Pat. application Ser. No. 463,329, now U.S. Pat. No. 3,956,245, describes a process for the bulk copolymerization of certain monoethylenically unsaturated compounds denoted as (A), (B), (C), (D), (E), and (F) (all as hereinafter more particularly defined) in bulk at temperatures above 150.degree. C in which gradual addition of component (B), a vinyl aromatic hydrocarbon such as styrene, is essential to control the rate of polymerization of the other components, in particular while component (A) is a vinyl ester of saturated monocarboxylic acids as hereinafter defined, and in which at least part of component (A), and optionally component (F), should be precharged.
Accordingly, insofar as the disclosure of U.S. Ser. No. 463,329 now U.S. Pat. No. 3,956,245 is relevant, such disclosure is incorporated herein by reference.
It has now been found that improved product performance can be obtained when from the polymerizable compounds only component (F) (as hereinafter defined) is precharged, and the other monomers are added at a reaction temperature above 150.degree. C in two stages as defined hereinafter. For use as a binder in non-aqueous coating dispersions, for example, the new improved process enables a higher solids content at spraying viscosity, as a result of lower viscosity of the dispersions.